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Refrigerants and Charging
			This is but one of many types of access valves. 

Most are pretty easy to figure out, though, if you understand this one. 
You use an "Allen" wrench to screw this plunger down (closed) and unscrew 
it to open. Normally, you will not need to do any of this because screwing 
the hose onto the port on the side will give you the pressure reading you 
			pic of service port

When you remove the hex cap on the service valve, you find a female hex 
opening to allow the moving of the internal plunger that blocks the flow 
of the refrigerant inside the copper lines. The main purpose of the liquid 
line valve plunger is to pump-down the system and, of course, it is closed 
during shipping and storage.  

If you close (rotate clockwise) you can stop the flow of refrigerant at this 
valve plunger and pump all the refrigerant into the condenser section and 
thus be able to work on the  rest of the system with no refrigerant in it.

You do this procedure while running the system.  Let it run for a bit to 
become stable and then close the liquid line valve plunger. The refrigerant 
can no longer get past the valves plunger and the compressor will suck the 
refrigerant from the rest of the system, pump it into the condenser and 
refrigerant will be stopped by the valve plunger on the other end of the 
condenser coils.

Watch the gauge pressures and when they both get NEAR the zero pounds, 
stop the unit and the pressures should remain as you last saw it (while 
it was running).  All the refrigerant is in the condenser.

The plunger holds it at one side of the condenser coil and the discharge 
valves inside the compressor should hold the other side of the condenser 
pressure from coming back into the compressor. This will hold all the 
refrigerant in the condenser and will leave no pressure on the compressor 
crankcase, suction line, evaporator and the liquid line (from the cooling 
coil to the condenser liquid valve plunger that is closed).

If the pressures begin to creep back up, then the liquid line valve
plunger is leaking or not closed well. Or, the discharge valves inside the
compressor may be cracked or broken. You can quickly close the plunger on
the suction line (if the problem is the compressor valves) as soon as you 
turn off the unit from running and it will at least confine the leaking 
pressure to the compressor (and of course the condenser coils).

This should explain the need (or convenience) for the existence of the
service port plungers.
TIP:Three kinds of complications can occur when attempting to pump-down a system.
  • The unit may shut off prematurely during the pump-down if there is a LOW PRESSURE CONTROL in the condensing unit. It will sense the pressure of the low side and will open the electrical circuit to the contactor as it senses a 2 to 20 pound pressure. The set point of the pressure sensing is variable, depending on the manufacturers wishes.

    To get around this, you can either temporarily bypass the control or you may be able to manually hold in the contactor points by pushing in on its slide bar that will depress the contact points. Simply let it back up when you reach the end of the pumping down of the unit and your pressures have reached the near zero level.

  • The second problem you may have occur is with the compressors INTERNAL REFRIGERANT BY-PASS VALVE. The purpose of this valve is to prevent the high side pressure from becoming too great. It by-passes the pumped high pressure back into the lowside of the system to prevent bursting, etc.
    • It will sense excessive high pressure that may be caused by a malfunction of the flow of hot gas refrigerant as it leaves the compressor (typically a malfunctioning 4-way valve on heatpumps). This is not very common, but does occur.
    • Secondly, it will sense a liquid-packed condenser coil (remember you cannot compress a liquid) caused by a refrigerant overcharge of the system. Or, you may have a large volume lowside system that is too much volume for the condenser. If this is the problem that opens the by-pass valve, then the condenser is full and will not hold the rest of the refrigerant in the system.

      Most likely, you have a system that has been over charged. You need to RECOVER the excess of refrigerant with an approved pump and container. You may need a professional for this. While he is there, let him find the cause of the overcharge.

  • Even a third possibility exists that may shut down the system prematurely. It is the existence of a HIGH PRESSURE SWITCH in the condensing unit.

    During a pump-down, the high side pressure will temporarily elevate some and then become very much lower than normal, but will not normally trip a high pressure switch at its highest point. Check the setting of the pressure switch, if you are able, or watch the pressure on the gauge when it shuts off.

    • The switch may be faulty,
    • the fan may not be running,
    • or the condenser may be excessively dirty.
    The unit pressure should never exceed 350 pounds during a pump down even on a very hot day with a refrigerant 22 system.
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